1. Field of the Invention
The present invention relates to elastic wave devices preferably for use in resonators and band-pass filters and more specifically to an elastic wave device using plate waves and a method for manufacturing the same.
2. Description of the Related Art
Hitherto researchers have proposed elastic wave devices that employ different elastic waves such as Rayleigh waves or SH (shear horizontal) waves. Japanese Unexamined Patent Application Publication No. 2008-530874 discloses an elastic wave device that uses plate waves.
The elastic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2008-530874 has a silicon substrate, an acoustic reflector on the silicon substrate, and a piezoelectric film on the acoustic reflector. IDT (interdigital transducer) electrodes are disposed on the piezoelectric film. The acoustic reflector is a mirror formed of alternately stacked high-elastic-impedance and low-elastic-impedance films. As an example of the combination of high-elastic-impedance and low-elastic-impedance films, the publication illustrates an acoustic reflector formed of alternately stacked tungsten and aluminum films.
The acoustic reflector of the elastic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2008-530874 is formed of tungsten and aluminum films, i.e., metallic films. In this configuration, unfortunately, the poor temperature characteristics of the metals lead to poor frequency-temperature characteristics of the elastic device.